WASHINGTON — The gathering at Joey’s Bar & Grill in Worcester drew little public notice. Over bar snacks, Representative James McGovern introduced Representative Edward J. Markey to his top supporters — union chiefs, local Democratic activists, student leaders, and other Central Massachusetts players who could prove valuable in Markey’s bid for US Senate.

Not long after the February event, McGovern received a call from Markey’s rival in the Democratic primary, another colleague and ally in Congress, Representative Stephen Lynch.

Lynch’s tone was friendly, but his gesture carried a veiled objection: What gives?

The call, confirmed and described by Lynch and two Democrats who requested anonymity, underscores family tensions, generated by the Senate primary, that are rattling through the state’s all-Democrat delegation in Washington.

The delegation already lacked some of the cohesiveness and camaraderie that were hallmarks of the leadership of the late Representative J. Joseph Moakley and the late Senator Edward M. Kennedy. The rituals that bonded the team in the past, such as regular meals at the Hunan Dynasty, a second-floor establishment on Pennsylvania Avenue near the Capitol, have faded. A rare public display of sniping, accompanied by private grumbling, followed the last House redistricting.

And now the Democratic Senate primary pitting Markey and Lynch against each other has made things considerably more awkward.

Markey is the more liberal of the two men and has served in the House longer than his Massachusetts colleagues — more than 36 years — and three times longer than Lynch, who is by some accounts a more isolated figure within the group. Lynch, though, represents a valuable Democratic constituency, South Boston, and has ties with some colleagues, including Representative Michael E. Capuano of Somerville, who serves another district with a similar urban Democratic core.

The primary campaign to run in a special election to replace John F. Kerry has been civil thus far, even tame by the standards of Massachusetts politics. Neither side has aired negative ads, and their initial debate last week was insult-free.

No sitting member has endorsed either candidate, but at least one Washington official familiar with the evolving dynamics said that could change if polls, which show a double-digit lead for Markey, tighten.

But the contest creates inevitable strain. Mayor Thomas M. Menino cracked a joke about the discomfort as Lynch and Markey sat one seat apart — with Representative John Tierney between them — during the State of the City in January.

“Are you strong enough to hold them back, both of them?” Menino quipped to Tierney.

Markey is by tradition considered the dean, in charge of rallying the delegation. He inherited the job in 2001, upon the death of Moakley, the South Boston Democrat who had held the post since the late 1980s. Now he is actively campaigning to defeat one of its members.

“You got two friends running,” said one member of the delegation, who requested anonymity to discuss the delicate dynamic. “Campaigns, especially close elections, have a way of fraying personal relationships.”

Markey, in an interview, downplayed the potential strains, calling Lynch a friend and pointing to the delegation’s agreement on key issues affecting the state.

“We have been united on everything over the years and I’m proud of that,” Markey said.

One Democratic official familiar with the delegation’s inner workings said members who might support Markey are wary of alienating Lynch. Lynch has reminded his colleagues that, regardless of who wins the primary and the special general election in June, both he and Markey will still be representing Massachusetts in Washington. If a Republican wins the seat, Lynch and Markey would retain their House seats; if Lynch or Markey prevails, the winner would remain in the delegation as a senator.

Lynch, who said he has been an ally and friend of McGovern’s for 30 years, said he called McGovern about the Joey’s Bar & Grill event because he wanted to find out what happened.

“He said it had been planned before I entered the race,” Lynch said. “I said I had no problem.”

McGovern then volunteered that he did not endorse Markey at the event, but McGovern made no promises about the future, Lynch recalled.

By then, rumors of a McGovern endorsement of Markey had trickled through party circles in Central Massachusetts, according to a Lynch campaign staffer who requested anonymity. In a related development, a local Democrat who had agreed to work as Lynch’s Central Massachusetts coordinator backed out three hours after she was offered the job, because of her loyalty to McGovern and the perception he would endorse Markey, the Lynch staffer said.

The jockeying follows four years of major transition in the state’s Washington leadership: Kennedy died of brain cancer in 2009; Republican Scott Brown exploded on the scene as Kennedy’s replacement, then gave way to Democrat Elizabeth Warren; Barney Frank and Western Massachusetts Representative John Olver opted to retire as the congressional districts were redrawn following the 2010 census; and Kerry moved up to secretary of state.

Any excessive divisivness during the current rebuilding phase could damage the state at a time of increasing competition for federal dollars. If Markey wins the race to replace Kerry, the unofficial duties of dean would fall to Representative Richard E. Neal of Springfield, who promised in an interview to more aggressively promote a bygone esprit de corps.

The standard for close relationships among the Massachusetts members may have been set by Representatives Thomas P. “Tip” O’Neill Jr. and Edward P. Boland, who represented opposite ends of the state in Cambridge and Springfield but shared an apartment in Washington. Neal and Meehan roomed until 2007, when Meehan left Congress. Lynch said he stayed on an inflatable bed for four months in Capuano’s Washington apartment when he was first elected in 2001.

Recently, redistricting tested some of the bonds within the delegation and set off grumbling — both public and private. Some members felt that Markey used his clout to protect his district at the expense of his colleagues, and there was talk that Moakley might have handled it better. (For all the nostalgia, relations were not always perfect in the Moakley era, either. He and Meehan, for example, had a public spat over several issues, including a Pentagon facility Meehan wanted in his district.)

Frank aired his frustration with Markey’s role in redistricting in public in November 2011. Then late last year, hard feelings lingering, he told the Globe he did not want his colleagues to throw him a going-away party. But Frank appears to have gotten over his wounds and has endorsed Markey, one of his oldest political friends.

Former Representative William D. Delahunt said Moakley’s leadership “was like having your guardian angel there. He was always looking after people.”

Markey is effective as dean, but more issue-oriented, added Delahunt, who is close to Lynch.

Still, Markey seldom gathers the delegation for formal meetings and meals, as Moakley was known to do at the Hunan Dynasty or in the “Massachusetts Room” at a former Legal Sea Foods. Instead, the group tends to meet informally in clusters on the House floor.

But regardless of who is leading them, congressmen are notoriously difficult to herd.

“These are titles only,” Delahunt said. “You have strong personalities. Barney, that’s beyond being a strong personality, and I was no shrinking violet either.”